Low common mode driver

Abstract

Techniques to provide a replica bias circuit for a high speed and low voltage common mode driver. In an embodiment, a pre-driver is coupled to provide driver input voltages to the driver, which driver includes a set of circuit elements coupled to provide, based on the driver input voltages, an output signal of a differential output. In another embodiment, a regulator circuit is coupled to provide regulated power to the pre-driver and driver, where the regulator circuit includes a scale replica circuit having a replica of the first set of circuit elements.

What is claimed is: 
     
       1. A transmitter comprising:
 a pre-driver coupled to receive a data signal and to output driver input voltages based on the data signal; 
 a driver coupled to the pre-driver, the driver including a first set of circuit elements coupled in series with one another, wherein the first set of circuit elements are coupled to provide a first output signal of a differential output based on the driver input voltages; and 
 a first regulator circuit coupled to provide regulated power to the driver, the first regulator circuit including:
 a first transistor coupled between the driver and a supply voltage rail; 
 a scale replica circuit having a replica of the first set of circuit elements; and 
 an error amplifier, wherein the scale replica circuit and the first transistor are both coupled to an output of the error amplifier, wherein the scale replica circuit is coupled to provide a feedback voltage to the error amplifier, wherein the error amplifier is coupled to amplify a difference between the feedback voltage and a reference voltage. 
 
 
     
     
       2. The transmitter of  claim 1 , the first set of circuit elements having:
 a second transistor coupled to the first output signal; 
 a first resistor coupled between the second transistor and the first output signal; and 
 a third transistor coupled to the first output signal. 
 
     
     
       3. The transmitter of  claim 2 , wherein a second resistor is coupled between the third transistor and the first output signal. 
     
     
       4. The transmitter of  claim 1 , wherein the driver includes a second set of circuit elements coupled in series with one another, the second set of circuit elements coupled to provide a second output signal of the differential output, wherein the second set of circuit elements are coupled in parallel with the first set of circuit elements. 
     
     
       5. The transmitter of  claim 1 , wherein the scale replica circuit is one-fourth scale replica of the first set of circuit elements. 
     
     
       6. The transmitter of  claim 1 , wherein a gate of the first transistor and a gate of a transistor of the scale replica circuit are coupled to the output of the error amplifier. 
     
     
       7. An imaging device comprising:
 a pixel array; 
 readout circuitry to generate image data based on signals from the pixel array; and 
 a transmitter coupled to the readout circuitry to transmit the image data, the transmitter comprising:
 a pre-driver coupled to receive a data signal and to output driver input voltages based on the data signal; 
 a driver coupled to the pre-driver, the driver including a first set of circuit elements coupled in series with one another, wherein the first set of circuit elements coupled to provide a first output signal of a differential output based on the driver input voltages; and 
 a first regulator circuit coupled to provide regulated power to the driver, the first regulator circuit including:
 a first transistor coupled between the driver and a supply voltage rail; 
 a scale replica circuit having a replica of the first set of circuit elements; and 
 an error amplifier, wherein the scale replica circuit and the first transistor are both coupled to an output of the error amplifier, wherein the scale replica circuit is coupled to provide a feedback voltage to the error amplifier, wherein the error amplifier is coupled to amplify a difference between the feedback voltage and a reference voltage. 
 
 
 
     
     
       8. The imaging device of  claim 7 , the first set of circuit elements having:
 a second transistor; 
 a first resistor coupled between the second transistor and the first output signal; and 
 a third transistor coupled to the first output signal. 
 
     
     
       9. The imaging device of  claim 8 , wherein a second resistor is coupled between the first output signal and the third transistor. 
     
     
       10. The imaging device of  claim 8 , wherein the driver includes a second set of circuit elements coupled in series with one another, the second set of circuit elements coupled to provide a second output signal of the differential output, wherein the second set of circuit elements are coupled in parallel with the first set of circuit elements. 
     
     
       11. The imaging device of  claim 7 , wherein a gate of the first transistor and a gate of a transistor of the scale replica circuit are coupled to the output of the error amplifier. 
     
     
       12. A transmitter comprising:
 a pre-driver coupled to receive a data signal and to provide driver input voltages based on the data signal; 
 a driver coupled to the pre-driver, the driver including a first set of circuit elements coupled in series with one another, wherein the first set of circuit elements are coupled to provide a first output signal of a differential output based on the driver input voltages; 
 a first regulator circuit coupled to provide regulated power to the pre-driver, the first regulator circuit including:
 a first transistor, wherein the pre-driver is coupled to a supply voltage via the first transistor; 
 a scale replica circuit having a replica of the first set of circuit elements; 
 an error amplifier; and 
 a first amplifier, wherein an output of the error amplifier and an output of the first amplifier are both connected to the first transistor, wherein the scale replica circuit is coupled to provide a feedback voltage to the error amplifier, wherein the error amplifier to amplify a difference between the feedback voltage and a reference voltage, and wherein the scale replica circuit is further coupled to a feedback loop extending from the transistor back to the first amplifier. 
 
 
     
     
       13. The transmitter of  claim 12 , wherein the first set of circuit elements includes:
 a second transistor; 
 a first resistor coupled between the second transistor and the first output signal; and 
 a third transistor coupled to the first output signal. 
 
     
     
       14. The transmitter of  claim 13 , wherein the replica of the first set of circuit elements includes a fourth transistor corresponding to the third transistor, and wherein the replica circuit is coupled to the feedback loop via the fourth transistor. 
     
     
       15. The transmitter of  claim 14 , further comprising a second regulator circuit coupled to the first regulator circuit via the fourth transistor, the second regulator circuit coupled to provide regulated power to the driver. 
     
     
       16. The transmitter of  claim 14 , wherein the fourth transistor further coupled to conduct current directly from the supply voltage according to a voltage of the feedback loop. 
     
     
       17. The transmitter of  claim 13 , wherein a second resistor is coupled between the third transistor and the first output signal. 
     
     
       18. The transmitter of  claim 12 , wherein the first amplifier is coupled to provide an output representing a difference between a reference voltage and the feedback voltage.